After being transported to the processing plant, the wet sand and gravel raw feed is stockpiled or emptied directly into a hopper, which typically is covered with a "grizzly"ofparallel bars to screen out large cobbles and boulders. From the hopper, the material is transported to fixed or vibrating scalping screensby gravity, belt conveyors, hydraulic pump, or bucket elevators. The scalping screens separatethe oversize material from the smaller, marketable sizes. Oversize material may be directed to a crusher for size reduction, to produce crushed aggregate. Crushing generally is carried out in one or two stages, although three-stage crushing may also be performed. Following crushing, the material is returned to the screening operation for sizing. The material that passes throughthe scalping screen is fed into a battery of sizing screens, which generally consists of either horizontal or sloped, and either single or multideck, vibrating screens. Rotating trommel screens with water sprays are also used to process and wash wet sand and gravel. Screening separatesthe sand and gravel into different sizeranges. Water 

### is sprayed onto the material throughoutthe screeningprocess. Afier screening, the sized gravel istransported to stockpiles, storagebins, or, in some cases, to crushersby belt conveyors, bucket elevators, or screw conveyors. The sand is hd from clay and organic impuritiesby log washers or rotary scrubbers. After scrubbing, the sand typically is sized by water classification. Wet and dry screeningisrarely 

### used to sizethe sand. After classification,the sand is dewatered using screws, separatorycones, or hydroseparators. After processing, the sand is transportedto storage bins or stockpilesby belt conveyors, bucket elevators, or screw conveyors.


### 1.2 Concrete

## atc chin^^,^

Concreteis composed essentiallyof water, cement, sand (fine aggregate) and coarse aggregate. Coarse aggregatemay consist of gravel, crushed stone or iron blast furnace slag. Some specialty aggregate products could be either heavyweight aggregate (of barite, magnetite, limonite, ilmenite, iron or steel) or lightweight aggregate (with sintered clay, shale, slate, diatomaceous shale, perlite, vermiculite, slag, pumice, cinders, or sintered fly ash). Concretebatching plants store, convey, measure and discharge these constituents into trucks for 

### transport to a job site. 

### In some cases, concrete is prepared at a building construction site or for the manufacture of concreteproducts such aspipes and prefabricated constructionparts. A generalized process diagram for concrete batching is included in Appendix 

### A of this document.

The raw materials can be delivered to a plant by rail or truck, but in the case of existing sources on GRIC land, they 

### are collocated with nonmetallic sand/gravel mining and processing facilities. The cement istransferredto elevated storage silos pneumatically or by bucket elevator. The sand and coarse aggregate are transfmed to elevated bins by front-end loader, clamshell crane, belt conveyor, or bucket elevator. From these elevatedbins, the constituents are fed by gravity
or screw conveyorto weigh hoppers, which combine the proper amounts ofeach material.

Truck mixed (transit mixed) concrete isthe process practiced at one of the existing GRIC concretebatch plants. At these plants, sand, aggregate, cement and water 

### are all gravity fed from the weigh hopper into the mixer 

### trucks. The concrete is mixed on the way to the site where the concrete is to be poured. Central 

### mix facilities (including shrinkmixed) constitute another concreteproduction process in use on GRIC lands. With these, concrete is mixed and then

NMMProcTSD 6-14-02 Created on 6/18/2002 9:39:00AM 2